What is Blood Pressure?

Blood pressure or BP results from two forces within the body’s arteries. One such force is created by the heart as it pumps blood into the arteries. The second is the force of the arteries themselves as they resist the blood flow.

When the heart pumps, it forces blood through the large arteries into the smaller arteries or arterioles. The arterioles can contact or expand, thus altering resistance to blood flow. This affects the amount of actual flow and its pressure. If the arterioles contract, the resistance to flow increases, which reduces blood flow and increases the BP. On the other hand, with expansion or dilation of the arterioles, the opposite occurs. Therefore, changes in the inner diameter of the arterioles are important in regulating blood flow and pressure. If the arterioles remain constricted, they can cause high blood pressure or hypertension.

How is blood pressure measured

Our BP is measured by a quick and painless test using a medical instrument called a sphygmomanometer. An inflatable cuff is wrapped around a person’s upper arm, just above the elbow and inflated. It compresses a large artery in the arm, momentarily stopping the blood flow.

Next, air in the cuff is released, and the person measuring the BP will listen with a stethoscope. When the blood starts to pulse through the artery it makes a sound. Sounds continue to be heard until the pressure in the artery exceeds the pressure of the cuff.

The person carrying out the test will listen and watch the sphygmomanometer gauge and record two measurements. Systolic pressure (the higher number) is the pressure of the blood flow when the heart beats. Diastolic pressure is the pressure between heart beats (the pressure when the last sound is heard). BP is measured in millimeters of mercury, which is abbreviated with mm Hg.

What is High Blood Pressure?

High BP in an adult is defined as systolic pressure of 140 mm Hg or higher and/or a diastolic pressure of 90 mm Hg or higher for an extended amount of time. A systolic pressure of 120 to 139 mm Hg or a diastolic pressure of 80 to 89 mm Hg is classified as prehypertension and needs to be watched carefully. A BP being less than 120 over 80 mm Hg is considered normal for adults.